Rice bran wax: a novel ingredient to structure
edible oils
Vincenzo di Bari, Tim Foster, and Bettina Wolf
University of Nottingham, Food Sciences, Sutton Bonington Campus, Loughborough,
LE12 5RD
Introduction
Oleogels preparation
One of the main challenges being faced by the food industry is the
reduction of trans and saturated triglycerides, i.e., the main ingredient
used to provide structure to liquid oils. These change is driven by
evidences suggesting that the consumption of these fats increases the risk
of cardiovascular diseases and Type II diabetes.. One of the novel route to
obtain solid-like fat is represented by the use of the so called
“organogelators”. These molecules provide solid-like structure to oils
although containing little amounts of saturated fatty acids1. Among
organogelators, rice bran wax (RBW) has proved to be one of the most
promising novel ingredient due to its ability to structure oils at very low
concentrations. Furthermore, RBW is produced in large quantities as byproduct of rice bran oil production (Fig. 1).
Granules of RBW were added to sunflower oil (SFO) to the desired
concentration (wt%) (Fig. 3a). Oleogels were prepared by heating
the RBW and sunflower oil mixture to 90 °C (Fig. 3b and c)
followed by cooling to ambient temperature (~25 °C ) (Fig. 3d).
Heat to
90 C
a
Cool to
25 C
Hold at
90 C
c
b
d
Fig. 3: Visualisation of RBW granules in SFO (a), melting of the wax granules (b) to obtain a clear liquid oil (c), and RBW based oleogel (1%, wt%)
Rice 1
Oleogels Macroscopic Behaviour
= 700 million metric ton
RBW appears as a pale yellow pellet material
(Fig. 2a) with a melting point of ~80 °C (Fig.
2b) (crystallisation ~78 °C ).
Rice bran
8% kernel
Rice bran
crude oil
60
a
Heat Flux (mW)
b
RBW
meltingat 10 °C min-1
RBW melting
50
40
30
Enthalpy of
Melting
(J g-1)
209.7
Onset T (°C)
77.1
RBW (%)
The minimum concentration
of wax to obtain a selfstanding gel (i.e., which does
not flow when inverting the
vial) is 0.5% (wt%) (Fig. 4).
1. Dewaxing:
cooling + c entrifugation
2. Degumming
3. Deacidification
Rice bran wax (1 -4% oil)
20
10
Peak T (°C)
81.2
End T (°C)
87.9
= 35.000 metric tons/ year
4 . Bleaching
5. Deacidification
0
30
40
50
60
70
Temperature ( C)
80
90
Fig. 4: Visualisation of RBW oleogels produced at increasing RBW concentrations.
At concentration above 5% (wt%) the oleogels
behaves as a solid-like material which can molded
(Fig. 5)
Rice bran
oil
100
Fig. 2: Visualisation of RBW granules (a) and melting profile of a bulk wax granules at 10
°C/min (b). The values of temperature and enthalpy of melting are provided in the table.
Fig. 1: Flow diagram of rice bran wax production
Fig. 5: Example of a solid-like oleogels produced
using 5% RBW
Oleogels Microstructural Properties
Oleogels Microstructure Visualisation
Oleogels Thermal Behaviour
12
Thermal behaviour was characterised using
a micro-DSC at 1 °C/min from 10 to 100
°C. 1% RBW oleogel shows thermoreversible behaviour: on multiple meltingcrystallisation cycles, curves perfectly
overlap (Fig. 6). Values of enthalpies and
peak of phase transitions are referred in
Table 1.
10
6
4
2
0
-2
Endo down
-4
-6
10
20
30
40
50
60
70
Temperature ( C)
80
90
Melting
100
Crystallisation
Fig. 6: Melting (downward) and crystallisation (upward) curves of 1% RBW
oleogel. The graph contains two melting and crystallisation curves, respectively.
Enthalpy
(J/g)
2.451
(±0.01)
-2.442
(±0.001)
Onset T
(°C)
55.56
(±0.02)
54.76
(±0.01)
Peak T
(°C)
62.23
(±0.06)
53.53
(±0.00)
End T
(°C)
65.71
(±0.02)
51.02
(±0.01)
Tab. 1: Melting and crystallisation parameters obtained for 1% RBW oleogel.
Values are average and standard deviation of duplicate, respectively.
Oleogels Elastic Properties
Network elasticity (G’) evolution over time at
various temperatures for 1% RBW oleogel (Fig. 8).
The elasticity of the network decreases significantly
at T ≥ 40 °C where some of the crystals may start
to melt. 30000
Amplitude sweep of 1% RBW oleogel at
20 and 50 °C (Fig. 9). The gel produced
at 20 °C shows higher G’and a larger
elastic region than gel produced at 50 °C.
100000
10000
G', G'' (Pa)
20000
15000
1000
10000
G' (20 C)
G' (30 C)
5000
G' (20 C)
100
1,000
2,000
3,000
4,000
Time (s)
Fig. 8: G’ evolution over time for 1% RBW olegel at different .temperatures (see
legend) using a shear strain of 0.01% and frequency of 10 rad/s
G'' (20 C)
Results of this research suggest that RBW can be used as
promising alternative to saturated fats for the structuring of
edible oils, where the structuring elements have needle-like
shape. In agreement with literature data1, oleogels show to
be thermoreversible viscoelastic materials.
Work currently undergoing is investigating the effect of
cooling rate and application of shear on oleogel formation
and mechanical properties. Incorporation of oleogels into
emulsions is also being investigated.
G'' (50 C)
G' (50 C)
0
Fig. 7: Polarised light image of a 3% (wt%) RBW oleogels produced at increasing
RBW concentrations
G' (50 C)
G' (40 C)
0
100 µm
Conclusions and undergoing work
25000
G' (Pa)
Heat flow (mW)
8
In Fig. 7 a polarised light
image of the microstructure
of a 3% (wt%) RBW oleogel
is shown. The crystals
(bright
elements)
are
dispersed through the oil
(dark areas) and have a
needle-like or fibrous shape.
This crystal morphology is
believed to be responsible
for the efficiency of RBW in
forming oleogels
10
0.001
0.01
0.1
1
Shear strain, γ (%)
10
100
Fig. 9: Elastic (G’) and viscous (G’’) of 1% oleogels at 20 and 50 °C
(frequency = 10 rad/s)
References: 1Blake AI, Co ED, Marangoni AG (2014) Structure and Physical properties of Plant Wax Crystal Networks and their relationship to Oil
Binding Capacity. J Am Oil Chem Soc 91: 885-903